OS X (Apple)

$ gcc filename.c -o filename

$ gcc file1.c file2.c file3.c -o filename

$ gcc -c file1.c ; gcc file2.c ; gcc file3.c
$ gcc file[123].o -o filename

# This file should be named makefile or Makefile, and be in the same
# directory as file1.c, file2.c, file3.c

# This variable is used by the predefined rule for converting .c into .o
# files.  You don't need to tell it to convert .c into .o, it assumes it when
# you tell it it needs .o files.  It feeds it into cc's commandline options.
# -Wall simply makes compiler warnings more verbose.
CFLAGS=-Wall

# This traditional variable tells the linker command below to link in the optional math library.
LDFLAGS=-lm

# $(CC):  Your default compiler.  You can change it if you want.
# $(LDFLAGS):  Linker options.  You can set these too.
# $^        All input files.  in this case file1.o file2.o file3.o
# $@        The output file.  In this case filename
# The rule itself says 'make filename from file1.o, file2.o, and file3.o'.
# The line below tells it how.
# Note the eight spaces in front of $(CC) should really be and MUST be a tab
filename:file1.o file2.o file3.o
        $(CC) $(LDFLAGS) $^ -o $@

$ make
cc -Wall   -c -o file1.o file1.c
cc -Wall   -c -o file2.o file2.c
cc -Wall   -c -o file3.o file3.c
cc -lm file1.o file2.o file3.o -o filename
$